The present invention relates to a heating device and a heated tool useful for working thermoplastic material.
Many consumer products now are marketed and packaged in thermoplastic film or bag packaging. Such product packaging oftentimes includes one or more holes for different purposes. For example, a hole can be formed in thermoplastic film shrink fit packaging to permit venting of air during subsequent sealing of the packaging. U.S. Pat. No. 5,140,133 describes a hot hole punch for this purpose where a heating element directly contacts and melts a tear-resistant hole in the thermoplastic film.
Also, thermoplastic bag packaging may include one or more holes in a sealed bag flange region by which the package is hung on a rack for display to purchasers. The hole(s) is/are adapted to receive a rod(s) of the display rack to hang the bag on the rack.
An object of the present invention is to provide a heating device constructed to provide distribution of heat to an axial end thereof.
Another object of the present invention is to provide a heated tool constructed to provide distribution of heat to an axial end of the tool to form a hole in or otherwise work a thermoplastic material when the end of the tool and the material are brought into contact.
The present invention provides a heating device to provide thermal energy and to a heated tool for working a thermoplastic material such as making hole in the material, heat staking the material or other working of the material. The heating device comprises a thermally conductive tubular body with a thermally conductive end closure disposed at an axial end of the tubular body, an electrical resistance heating element disposed in the tubular body and having an end spaced axially from the end closure, and a thermocouple disposed between the end of the heating element and the thermally conductive end closure. An outer protective tubular casing is disposed about the tubular body with an outer protective end cap disposed at an axial end of the tubular casing in contact with the thermally conductive end closure to receive heat therefrom by thermal conduction.
The heating element typically comprises an electrical resistance heating coil having a pair of thermocouple wires that extend through the heating coil. An electrical insulator typically is disposed between the thermocouple and the end of the heating coil. An electrical insulator also typically is disposed between the heating element and the tubular body. A heat reflective thermal insulator is disposed between the tubular body and the outer protective tubular casing.
In one embodiment of the invention, the end closure comprises a copper plug disposed in an open axial end of a copper tubular body. The outer protective end cap is metallurgically attached to protective tubular casing and includes a recess or concavity that is with a thermally conductive material, such as braze material. The material is shaped to form a flat axial working tip or end of a heated tool.
In one embodiment of the invention, the outer end cap and the end closure include a threaded bore in which a threaded shaft of hole punch is threaded.
In another embodiment of the invention, the tubular casing includes a threaded outer periphery or circumference at its axial end, and an internally threaded hole punch is threaded on the threaded periphery.
A machine for hole punching, heat staking or other material working can include a tool support member and at least one heated tool of the type described above disposed on the tool support member in a manner that the hot tool end or tip can be brought into contact with the thermoplastic material.
The objects and advantages of the present invention will become more readily apparent from the following description taken with the following drawings.